The present invention is related generally to medical devices. More specifically, the present invention is related to catheters for performing percutaneous myocardial revascularization (PMR) which is also referred to as transmyocardial revascularization (TMR). The present invention includes atraumatic tips for limiting unwanted penetration into the endocardium by outer tubes housing therapeutic tips within.
A number of techniques are available for treating cardiovascular disease such as cardiovascular bypass surgery, coronary angioplasty, coronary atherectomy, and stent placement. These techniques are generally performed to bypass or open lesions in coronary vessels to restore patency and increase blood flow to the heart muscle. In some patients, the number of lesions are so great, or the locations so remote in the coronary vasculature, that restoring coronary artery blood flow to the heart is difficult. Transmyocardial revascularization (TMR), also known as percutaneous myocardial revascularization (PMR), has been developed as an alternative to these techniques which are directed to bypassing or removing lesions.
Heart muscle may be classified as healthy, hibernating, and xe2x80x9cdead.xe2x80x9d Dead tissue is not dead but is scarred, no longer contracting, and no longer capable of contracting even if adequately supplied with blood. Hibernating tissue is not contracting muscle tissue but is capable of contracting again, provided it is once more adequately supplied with blood. PMR is performed by wounding the myocardium of the heart, often forming and leaving patent holes, and sometimes injecting angiogenic substances in the process.
PMR was inspired in part by observations that reptilian hearts are largely supplied by blood directly from within the heart chambers. In contrast, mammalian hearts are supplied by blood pumped from the heart, through the aorta, and back to the heart muscle through the coronary arteries. Positive results have been observed in some patients receiving PMR treatments. The positive results may be due in part to blood being perfused into the myocardium from within the heart chambers through holes into the myocardium. The positive results are believed to be due in part to a wound healing response of the myocardium which includes formation of new blood vessels in the heart wall, which are believed to connect with the heart chamber interior and/or other coronary blood vessels. The PMR procedure can include cutting into the myocardium with therapeutic tips or burning holes with therapeutic tips having laser or radio-frequency current tips. PMR therapeutic tips can also be used to inject angiogenic substances such as growth factors or genes selected to induce angiogenesis.
The PMR procedure generally involves insertion of a therapeutic tip such as a sharp cutting tip into the heart chamber or chambers selected for treatment. The cutting tip and associated inner shaft can be guided into the chamber within a guide catheter, which may have been inserted into the vasculature a long distance from the heart. After the inner shaft distal end exits the guide catheter, the cutting tip is preferably steered to several positions for formation of several holes in a pattern across the endocardium. In order to steer the inner shaft and cutting tip, an outer shaft or tube is sometimes disposed coaxially about the inner shaft and within the guide catheter. The outer tube can have structural features at the distal end for bending to various angles to reach various locations in the heart wall. The outer tube and inner shaft can be cooperatively advanced to bring the cutting tip into contact with the heart wall.
To allow passage through the guide catheter, the outer tube should have a sufficiently small radial or transverse profile over its length. As with many catheter devices, a small profile is desirable to allow passage through tortuous and narrow vessels. At the outer tube distal end however, a small profile can also mean a small profile presented to the heart wall when inserting a cutting tip. It may be desirable to bring the outer tube very close or even into contact with the heart wall. While inserting a cutting tip into the heart wall may be desirable, inserting the larger outer tube distal end into the heart wall may be undesirable.
What is desirable is an improved guide device for steering inner shaft cutting tips into position within the heart myocardium. The improved guide device would preferably include a distal end having a small profile for passage through a guide catheter, yet having a larger profile for presentation to the heart inner wall to limit undesirable penetration by the guide device distal end.
The present invention includes devices for performing percutaneous myocardial revascularization (PMR) that can lessen the likelihood of a shaft distal end penetrating undesirably into the myocardium. In one application, PMR devices are used to penetrate the endocardium and myocardium to a controlled depth. One group of devices according to the present invention includes an inner shaft having a therapeutic tip, for example, a distal cutting tip. The inner shaft can be disposed within an outer tube or shaft lumen, and the outer shaft can be disposed within the lumen of a guide catheter. Preferably, the myocardium is penetrated by the cutting tip of the inner shaft but not by any larger profile outer shafts or tubes disposed about the inner shaft. The outer shaft distal region preferably has a first configuration having a small radial extent or profile allowing disposition of the outer shaft within a small guide catheter. The outer shaft distal region preferably also has a second configuration having a larger radial extent or profile for presentation against the endocardium. While having the larger profile, the outer tube distal end has increased resistance to penetrating the heart wall. The larger surface presented to the heart wall while in the radially expanded position forms a more atraumatic distal end for the outer tube distal end.
The outer tube distal end can have an atraumatic distal hood or tip that is formed of an elastic material that can be benignly forced against an obstacle such as the heart chamber inner wall, the endocardium. The atraumatic hood allows passage of the therapeutic tip therethrough to contact the heart wall. The atraumatic hood preferably has a sufficiently small profile so as to fit within an enclosing guide catheter in a first configuration. In one embodiment, the atraumatic hood is sufficiently elastic to longitudinally foreshorten and radially expand to attain a larger profile or radial extent when forced against the endocardium. The radially enlarged hood presents a larger transverse surface area to the heart wall and inhibits penetration of the heart wall by the outer shaft distal end. In one embodiment, the atraumatic hood has a bulbous shape and has a distal-most orifice for receiving the cutting tip of a slidably disposed inner therapeutic shaft.
One outer shaft atraumatic tip includes a distally disposed elastic member having a first, constrained configuration, and a second, unconstrained configuration. In a constrained configuration, which may occur when the tip is constrained within an enclosing guide catheter, the tip has a radial extent or profile that fits within the guide catheter. In an unconstrained configuration, the tip can expand to a larger radial extent or profile, where the radial extent is preferably larger than the outer diameter of the guide catheter. One atraumatic tip includes an elastomeric disk or washer transversely disposed to the longitudinal axis of the catheter. Another atraumatic tip includes several radially disposed segments or arms. In use, the atraumatic tip can expand radially outward when advanced from a guide catheter, and can radially contract when retracted back within the guide catheter.
Another outer shaft atraumatic distal end or stop includes a spring wound about the outside of the outer shaft distal region. The spring preferably has a constrained configuration when contained within an enclosing guide catheter. When advanced distally from the guide catheter, the spring preferably expands radially to a second, unconstrained configuration having a larger profile. The larger profile can present a hindrance to penetration of the endocardium by the distal end of the outer shaft. After use of any inner therapeutic shaft, the outer shaft can be retracted within a guide catheter, again constraining the distal spring and reducing the radial extent. In one embodiment, the spring is formed as a helical coil. In another embodiment, the spring is formed as a ribbon or clock spring disposed about a relatively short length of the outer shaft.
One device outer shaft includes an atraumatic distal region formed as an inflatable member having a small, uninflated profile and a large, inflated profile. The shaft can include an inflation lumen and the inflatable member can include an inflatable balloon having an interior in fluid communication with the inflation lumen. The distal inflatable member can be inserted uninflated within a guide catheter for delivery to a target site such as the endocardium. After advancing the distal inflatable member from a guide catheter, inflation fluid can be supplied through the inflation lumen and into the inflatable member, thereby increasing the radial extent of the inflatable member. The inflated member or balloon can present a larger distal transverse surface area, which presents an inhibition to penetration of the endocardium by the outer shaft distal end. One device has a dual lumen shaft with side-by-side lumens. Another device has an inflation lumen coaxially disposed about an inner lumen which can be used for delivery of a therapeutic inner shaft.
One device has a distal cross member having a first, transverse orientation, and a second, more longitudinal orientation. The cross member is preferably pivotally mounted to a distal-most portion of the outer tube. The cross member can have a first arm for attachment to an elongate manipulation member and a second, opposite arm having an opening for allowing passage of a therapeutic inner shaft through the transversely disposed cross member. In one embodiment, the cross member is biased to remain in a substantially transverse orientation to the longitudinal axis of the outer tube. In one embodiment, the attached cross member arm can be either pushed or pulled with the elongate manipulation member. In some embodiments the elongate manipulation member is capable of effectively pulling the cross member to a transverse position, but not of pushing the cross member arm to a smaller profile, more longitudinal orientation. In other embodiments, the elongate manipulation member is capable of both pushing and pulling the cross member between small and large profile orientations.
In yet another embodiment, the outer tube has distally disposed wings or fins having a first, closed position, and a second, open position. In the closed position, the wings can lie closely about the outer tube distal region outer walls, presenting a small transverse profile. In the open position, the wings can extend radially outward, presenting a large transverse profile. The wings can be biased to expand to the larger profile configuration when unconstrained by a guide catheter. In one embodiment, the wings are formed of a shape memory material, for example Nitinol, and expand to the larger profile configuration when warmed to body temperature. In use, the wings expand to present a large profile to the endocardium or other surface. The wings can be forced to contract when the outer shaft distal end is retracted within a guide catheter having a smaller inside diameter than the radial extent of the distal wings.
In still another embodiment, the outer tube has a distal region which can be followed distally by a distal end which can be terminated more distally by a distal-most portion. The distal end can include an outer tube wall region having several longitudinally disposed slits or slots defining wing regions therebetween. The wing regions can include preferential folding locations. An inner tube or shaft can be slidably and coaxially disposed within the outer tube and secured to the outer tube distal most portion. The PMR device having the inner and outer tube can be distally advanced from a guide catheter and the inner tube moved proximally relative to the outer tube, thereby applying a proximal pulling force on the outer tube distal-most portion. The applied force can force the longitudinal wings between the longitudinal slots to buckle and splay radially outward, longitudinally foreshortening the outer tube distal end in the process. The radially outwardly splayed wings can present a larger radial extent or profile to the endocardium and inhibit penetration of the endocardium by the outer tube. After use, the inner tube can be advanced relative to the reduced profile device and retracted within a guide catheter.
In another embodiment a therapeutic catheter includes an outer tube having a distal region, a distal end, a tube wall, and a first lumen within the outer tube. The outer tube distal end is preferably sufficiently sharp to penetrate into the endocardium. A stop can be disposed within the outer tube, defining a smaller inside diameter region in a proximal portion of the outer tube distal region. A plug disposed within the outer tube first lumen distal region preferably has a maximum outer dimension too large to allow proximal movement past the stop. When the sharp distal end penetrates into the myocardium, the penetration is limited by the myocardium contacting the plug, which can in turn be contacting the stop or shoulder. The stop can be an annular stop, defined by an integrally formed annular stop in one embodiment and by the distal end of an inserted inner tube in another embodiment.
In one therapeutic catheter for increasing myocardial blood perfusion the outer tube wall has at least one substance delivery lumen disposed within and at least one injection port disposed near the outer tube distal end. In another therapeutic catheter an inner tube has a substance delivery lumen and a distal end, the inner tube being disposed within the outer tube. A plug having a lumen therethrough for receiving the inner tube can be slidably disposed within the outer tube, such that the inner tube distal end forms a distal shoulder for limiting proximal travel of the plug. In one embodiment, the inner tube distal end is sufficiently sharp to penetrate into the myocardium and extends distally past the plug when the plug abuts the shoulder.